1. Field of the Invention
The present invention relates to an inductive type thin film magnetic head used for a floating type magnetic head or the like, and more particularly, to a thin film magnetic head which can reduce eddy current loss without forming a secondary magnetic gap by improving the structure of a core layer, and a method of fabricating such a thin film magnetic head.
2. Description of the Related Art
FIG. 7 is a longitudinal sectional view of a conventional thin film magnetic head.
The thin film magnetic head shown in FIG. 7 is a so-called "combined magnetic head", in which a reading head, using a magnetoresistance effect, and an inductive magnetic head, for writing the signal into a recording medium such as a hard disk, are deposited. The combined magnetic head is provided on the end of a slider of a floating type magnetic head on the trailing side facing a recording medium such as a hard disk.
As shown in FIG. 7, an underlying layer 41, a lower shield layer 42, a lower insulating layer 43, a magnetoresistive element layer 44, and an upper insulating layer 45 are sequentially deposited on a substrate 40 composed of Al.sub.2 O.sub.3 --TiC, and an inductive magnetic head for writing is formed thereon.
A lower core layer 20 is composed of a magnetic material having high magnetic permeability such as an Fe--Ni alloy (permalloy). In a combined magnetic head in which the inductive magnetic head shown in FIG. 7 is sequentially deposited on a reading head using a magnetoresistance effect, the lower core layer 20 functions also as an upper shield layer for the reading head.
A gap layer 2 composed of a nonmagnetic material such as Al.sub.2 O.sub.3 (aluminum oxide) is formed on the lower core layer 20. An insulating layer 3 composed of a resist or other organic resin is formed on the gap layer 2.
A coil layer 4, composed of a conductive material having low electrical resistance such as Cu, is spirally formed on the insulating layer 3. Although the coil layer 4 is formed so as to go around a base 21b of an upper core layer 21, only a portion of the coil layer 4 is shown in FIG. 7.
An insulating layer 5 composed of a resist or other organic resin is formed on the coil layer 4. The upper core layer 21 is formed by plating a magnetic material such as a permalloy on the insulating layer 5. A tip 21a of the upper core layer 21 is joined to the lower core layer 20 with the gap layer 2 therebetween at the section facing a recording medium to form a magnetic gap having a gap length G11. Also, a gap depth Gd is determined by the depth of the tip 21a.
Also, the base 21b of the upper core layer 21 is connected to the lower core layer 20 through a hole formed in the gap layer 2 and the insulating layer 3.
In the inductive magnetic head for writing, when a recording current is applied to the coil layer 4, a recording magnetic field is induced to the lower core layer 20 and upper core layer 21, and a magnetic signal is recorded onto a recording medium such as a hard disk by means of a leakage magnetic field from the magnetic gap between the lower core layer 20 and the tip 21a of the upper core layer 21.
Although the recording frequency must be increased in order to meet the high-density recording, if the resistivity in the lower core layer 20 and the upper core layer 21 is low, eddy-current heat loss increases at high frequencies.
Therefore, the resistivity in the lower core layer 20 and the upper core layer 21 must be increased, and one of the known methods for increasing the resistivity is to change the structure of the lower and upper core layers 20 and 21 from a single layer to a laminate.
In accordance with Japanese Patent Laid-Open Nos. 63-244407 and 1-1027:12, as shown in FIG. 8, an upper core layer 21 (and/or a lower core layer 20) is formed of a laminate in which a nonmagnetic material layer 24 is interposed between magnetic material layers 22 and 23.
In such a laminate, eddy current loss can be reduced.
However, as shown in FIG. 8, the nonmagnetic material layer 24 is revealed to the surface (air bearing surface) facing a recording medium D, and magnetic gaps (secondary magnetic gaps) having a gap length G12 are formed by nonmagnetic material layers 24.
Accordingly, in the thin film magnetic head shown in FIG. 8, in addition to a magnetic gap having a gap length G11 by a gap layer 2, the magnetic gaps by the nonmagnetic material layer 24 (hereinafter referred to as "secondary magnetic gaps") are formed, resulting in unstable recording characteristics.
In particular, if a secondary magnetic gap is formed on the upper core layer 21, the secondary magnetic gap is located on the trailing side in relation to the original magnetic gap toward the recording medium D, and since the secondary magnetic gap is scanned after the original magnetic gap is scanned toward the recording medium D, the leakage magnetic field from the secondary magnetic gap largely affects the recording medium D.
Japanese Patent Laid-Open No. 63-247906 discloses a thin film magnetic head in which the structure of the tip of a core layer has been improved so as not to form a secondary magnetic gap in the core layer.
In the thin film magnetic head disclosed in the patent described above, as shown in FIG. 9, a nonmagnetic material layer 24 is formed in regions other than a region near a tip 21a of an upper core layer 21, and the nonmagnetic material layer 24 is not exposed at the surface facing a recording medium D.
By employing such a structure, no trouble is caused by secondary magnetic gaps, and because of the laminate in the regions other than the tip 21a, there is low eddy-current heat loss, enabling an improvement in recording characteristics at high frequencies.
However, since the nonmagnetic material layer 24 is not formed near the tip 21a of the upper core layer 21, the region near the tip 21a is single-layered, which increases eddy current loss near the tip 21a. Also, the fabrication process becomes significantly complex.